$ D = \left[\begin{array}{rrr}-1 & 0 & 3 \\ -2 & 4 & 4 \\ -2 & 0 & 3 \\ 0 & 2 & -1\end{array}\right]$ What are the dimensions of matrix $ D$ ?
Solution: The first dimension is the number of rows in the matrix. How many rows does $ D$ have? The second dimension is the number of columns in the matrix. How many columns does $ D$ have? So, $ D$ is a 4 $\times$ 3 matrix.